Synchronizing arrangement for picture transmission



Dec. 10, 1929. F. scHRbTER SYNCHRONIZING ARRANGEMENT FOR PICTURETRANSMISSION Filed NOV. 1927 2 Sheets-Sheet 2 84070 4100014 mum/rimIMfl/F/f/P INVENTQR Ffifll SCHROTER NEY Patented Dec. 10, 1.929

UNITED STATES PATENT orricr.

rmrz scnnornn, or BERLIN, GERMANY, assrenoa ro en snnnscnu'r' rfln,murm- LOSE TELEGRAPHIE m. 3. 1a., or BERLIN, GERMANY, A CORPORATION orGER- MANY SYNGHRONIZING ARRANGEMENT FOR PICTURE TRANSMISSION IApplication filed November 2, 1927, Serial No.

The present invention discloses a circuitarrangement adapted to insuresynchronization of apparatus for picture transmission or similarapparatus for communication work in a simple manner. The basic idea ofthe invention consists in that, with the use of one and the samecarrier. wave, and apart from the picture impulses or other signals, arhythm, cadence or synchronizing frequency for the drive of asynchronous motor at the receiving end is simultaneously transmitted bymodulating the carrier wave with two audio frequencies, one of which inturn is modulated by the picture-element or picture-point frequency orsignal frequency, while the second audio frequency is transmittednon-modulated. The said two audio frequency waves modulating the carrierfrequency in this scheme must be spaced so far apart that no disturbinginterference will result between' the said two audio frequencies whenrectified. Another essential point is that the audio frequency used forsynchronization modue lates the radio frequency only to a slight degree,and, if possible, only to an extent so that its intensity suflices forfurther amplifi cation in the receiver apparatus.

One embodiment of theidea underlying the invention is illustrated in theaccompanying drawing in connection with its application to picturetransmission, in which Fig. 1 illustrates a transmitting system, Fig. 2

v a receiving system adapted for cooperation I therewith, Fig. 3represents a modified form of the transmitter shown by Fig. 1, and Fig.4 represents a modification of the form of receiver shown by Fig. 2. d Ir Now making referenceto the accompanying drawings the picture ordocumentto be transmitted is placed on av drum 1 which is subject inwell known manner to a rotary and a shifting movement- A'photo-electriccell 2 ofannular form isadaptedto explore p I 1 of the transmission ofthe picture-point frethe picture by the aid of lightjfdiifuselyreflected from the picture surface. .';'For .=thi s,

, purpose, the light issuing from, luminous source 3 is passed in theshape of'a'shar-p pencil of li ht formed by the aid of a lens 4 throught e central portion'of the annular photo cell 2 adjacent the picturesurface. For

thetransmitter end, two low g'enerators' are provided, one of whichfurnishesa carrier wave for the icture-point' frequencies, while theother one] rnishes the synchronizing frequency. The former may 230,423,and in Germany "November 24, 1858.;

driving the drum 1 a motor 5 is provided and the rotation thereof istransmitted through a toothed gear wheel 6 tothe drum 1. At thereceiving end there is a drum 7 which corresponds to drum 1 at thesending end. The

drum 7 is arranged to revolve in\syncho-- nism with drum 1 and issubject to a similar displacement or shifting motion along its axis. Asthe means to control thelight striking a light sensitive film suitablefor record-- ing the received picture, a' Karolus cell 8 has here beenassumed. The cone of light which-passes between the condenser plates ofthe cell 8 is supplied from a light-source 9.

13. A'motor 15 and a convenient toothedgear wheel, similar to that ofthe'transmitter, is provided for driving-the drum 7.

The two motors 5 and 15, for instance, may

be of the shunt-wound direct current type,

and. their speedis adjusted by means of the series rheostats 16 and 17,respectively. However, it is a good plan to further provide for themotor 5 a speed governor (not shown) of any convenient kind, forinstance, a Giebe' t' pe centrifugal governor adapted to keep 't e"fluctuations ofthe speed of rotation inside acceptably low limits.However, at the receiving end the rotationof motor 15 by means of anadditional synchronous motor '36 is kept iH,. tep with that of the shaft'of motor 5. FThe transmission of the synchronizing audio frequencyoscillations from the transmitter to the synchronizing motor 36 (which,as to the rest, maybe of any de-' sired form, for instance, itmay-consist of a La Cour-wheel) is effected independently quenciesin thefollowing manner e eq n y be of any suitable kind, for instance, it mayconsist of a tuned thermionic valve generator, or a tuning-forkgenerator comprising amplification means, or else, as shown merely byway of example in the drawing, it may.

consist of an induction-type machine 18, the same in this case beingdrivenby a motor 5. Fundamentally speaking, an alternative scheme wouldbe to produce the picture-point carrier frequency by optical meansinstead of electrically by that, instead of 18, a revolving perforateddisk is placed in the path of the raysissuing from 3, the carrierfrequency being thus produced directly in the photoelectric cell 22,provided the speed of rotation and the number of holes are chosenconveniently. Hence, while the carrier frequency for the picture-pointimpulses may be produced alsoindependently of the motor 5 by a greatnumber of methods, the second audio frequency to be used forsynchronization must bear an invariable relationship to the speed ofrotation of the motor 5 or of the driving shaft, or in other words, itmust vary in direct proportion to the variation of the motor speed. Forthis purpose, a second inductor 19 positively coupled with 5 and mostsuitably seated upon the same shaft, 1s provided.

The carrier frequency or wave supplied from the generator 18 for thepicture-point frequencies is controlled or modulated in amplitude in thefollowing way by the light brought to act upon the photo-electric cell2: The photo-electric cell 2 forms the arm of a bridge arrangement whichfurther comprises a variable condenser 21 and resistances 22 and 23. Atthe terminals of one of the diagonals of the bridge is supplied analternating current potential furnished from the source 18 andconveniently regulated by a potentiometer 20. At the terminals of theother bridge diagonal thisfrequency subject to control of its amplitudeby the light brought to act .2 upon the cell 2, is taken as and fed tothe control electrode of the amplifier tube 24. The object of the bridgearrangement as stated is to completely compensate the capacitive currentflowing by way of the electrodes of the photo-electric cell 2 by the aidof condenser 21, so that, in the absence of illumination of the photocell 2, no carrier alternating current potential will act upon the gridof the tube 24:, it being understood, of

i course, that for the same purpose any other suitable compensationscheme could be employed. In series with the photo-electric cell theremay be, further, provided a direct current potential upon which thealternating current potential taken off at 20 is superposed. If, then, astate of balance 'is established in the bridge when the cell is dark,the balance will be disturbed as soon as light strikes the said cell 2,with the result that a certain amplitude of the frequency furnished from18 will arise at the control grid of the tube 24, the value of saidamplitude varying at the rhythm of the distribution of light an dark inthe explored picture, in other words,

the audio fre u'ency furnished from 18, in turn, is modu ated by thepicture-point or picture-element frequency resulting from the changes inlight and dark. If in the presence of the minimum illuminationcorresponding to be more precise, only to such an extent that, comparedwith the noises due to stray, a sufficiently audible sound is heard atthe rece1ver end, the latter being'then further amplified until itrepresents an energy adequately high for the operation of thesynchronous motor 36. In case it is not desired or it is impossible toobtain the full energy required for a synchronous motor 36 by means ofamplification, the audio frequency tone received need be amplified onlyto such an extent as is required to operate a synchronous switch bymeans of which, by the aid of oscillation or rotating contacts, theopening and closing at the proper rhythm of afeeding circuit of thesynchronous motor 36 is caused in the manner shown by Fig. 4. Easymodulation of the radio frequency of the transmitter. by the audiofrequency of the generator 19, according to the drawing, is effected bythe means of a transformer 26 connected in the grid circuit of the tube24, the primary current of said transformer being regulated to thedesired strength. The

battery 25 serves for providing the biasingpotential on the tube 24.Another method of transmitting the frequency of generator 19 to thecorresponding station, for instance, as showp by Fig. 3, consists inthat this frequency is used for heating the filament of a tube which maybe connected in the input amplifier cascade or the transmitter tubeitself in the case shown, the filament of the amplifying tube 24 of Fig.3 is heated from the generator 19 which is here shown as an alternator.The frequency is then intentionally transmitted to the receiver end inthe form of what is known as the filament tone, and the amplitudethereof is governed by the thermal inertia of the filament and by theadjustment of plate and grid biasing potential of the tube that is used,the amplitude being thus adjustable at will.

It is, of course, possible to introduce the frequency of generator 19also at some other point in the amplifier cascade between tube 24 andthe modulator 28 of the'radio frequency transmitter 29. In the drawinghere shown, the frequency of the generator 18 modulated by thepicture-element frequency f and the non-modulated wave of the generator19 operate at the proper amplitude re-- lations, as hereinbefore pointedout, upon the grid of the .tube 24, and they are further.

amplified by the photo-electric amplifier 27 until they have been raisedto the amplitude required for the control of the modulator tube. Asregards the diflerence infrequency of 18 and 19, it may be stated that,when 18 furnishes a carrier frequency of 5000 cycles, the one of19fmaybe chosen at from 200 to 500 cycles. Assuming that at the transmissionrate chosen, there is no need for recording picture-point frequenciesabove 2000' 'the same kind could anyway be rendered harmless by thefilter circuits'employed at g the receiver end.

At the receiving end, as shown by Fig. 2, there is first provided thewireless receiver 30 which may be worked in any suitable manner withradio frequency amplification or with intermediate-frequencyamplification, and which comprises further means for demodulation of theradio frequency oscillations. In the demodulation there is obtained amixture of the two audio frequency oscillations furnished from sources18 and 1 9 at the transmitter station, theformer one representing theband formed by the picturepoint frequencies. After suflicientpreliminary amplification in the audio frequency amplifier 31, the bandcontaining the picturepoint frequencies 'is separated from thesynchronizing wave by means of filters 32 and 33. In a simple case, itwould also be sufiicient to replace one of said filters,that is, 33adapted to pass the higher frequencies by a condenser chain, while theother one, 32,

adapted to pass the lower synchronizing frequency by a coil chain, or ahigh-pass and a a to the requisite amplitude by amplifiers 34.

low-pass, respectively. The two frequencies thus separated are thereuponraised finally and 35, respectively. The Karolus light valve is unitedwith amplifier "35 in wellknown manner, while the synchronous motor 36is connected with the output circuit of amplifier 34. An alternativescheme, as

alternating current power ated for the motor '36.

I claim:

"1. Ina facsimile. system, a light sensitive relay, means forintroducing-a carrier frequency potential in the output circuit of saidrelay, means for translating varying intensities of light and shade in afacsimile to be is locally gener-' transmitted into varying intensitiesof cur-- rent through said relay "and modulating said carrierfrequencythereby, a vacuum tube amplifier for amplifying said modulatedcarrier frequency, means for producing a separate synchronizingfrequency, means for applying said synchronizing frequen'c to thefilament member of said vacuum tu e amplifier for heating the same andtransmitting the said synchronizing pulse as a filament tone, means fortransmitting said facsimile modulated carrier and said synchronizingenergy, means for receiving said transmitted signals, and.

means at the receiving point for separating the facsimile modulatedsignals and the synchronizing-signals and controlling a receiving systemtherefrom.

2. In a facsimile system, a support surface .for a facsimile to betransmitted,"a photo cell and means for influencing the photo cell bylight varied in accordance with the intensity of light and shade in thefacsimile to be transmitted, a bridge structure having the said photocell forming one of the legs thereof, an adjustable capacity member inan adjacent leg thereto for balancing the capacity of the said photocell during periods of zero illumination thereon, means for producing acarrier frequency, means for introducing said carrier frequency in saidbridge structure across the diagonal between said cell and said variablecapacity, means provided by said photocell for modulating said carrierfrequency, means for producing a separate synchronizing frequency, anamplifier, means for amplifying both said modulated carrier and saidsynchronizing frequency by said amplifier, means for transmitting eachof said energies, means for receiving the said transmitted energies,means at the receiving point for distinguishing between thesynchronizing energy and the picture frequency energy, and means forutilizing the picture frequency energy to produce at the receiverareproduction of the transmitted facsimile, and means for utilizing thesynchronizing energy for producing synchronous operation of the receiverand the transmitter.

3. In a facsimile system,'a sup ort surface for a facsimile to betransmitted, a photo cell and means for influencing the photo cell bylight Varied in accordance with the intensity of light and shade in thefacsimile to be transmitted, means for generating electricaloscillations of a carrier frequency,

means provided by said photo cell for modulating the output of saidgenerating means, means for generating a separate synchronizingfrequency differing from the modulating frequency, an amplifier andmeans for applying oscillations of said carrier frequency, saidmodulation frequency and said synchronizing frequency to the inputthereof, and means associated with the output circuit of said amplifierfor transmitting the resultant output energy.

FRITZ SCI-IROTER.

